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Hash Map In Python

Hash Map In Python


Hash maps are indexed data structures. A hash map uses a hash function to compute an index with a key/value into an array of buckets. Its value is mapped to the bucket with the corresponding index. The key is unique just like a currency note and these keys are immutable.


Think of a cabinet having drawers with labels for the items stored in them. Here,

  • The cabinet is the hash map.
  • The drawers with labels are the buckets.
  • The user’s email or User ID is the key.
  • The user’s details such as name, bank number, contact number are the values.
  • These values get mapped to the buckets.


The fundamental implementation of a hash map is done using a Hash function. It accepts a key and translates it to the index of a bucket in the bucket list. Each and every key must have a different index in Ideal Hashing. However, the collisions (When hashing gives an existing index) still may occur. We can use rehashing techniques or maybe a bucket to store multiple values by appending a list.


In Python, dictionaries are examples of hash maps.


The hash map design will include the functions that follow:

set_val(key, value): Enters a key-value pair into the hash map. If the value already exists in the hash map, it updates the value.

get_val(key): Returns the value to which the specified key is mapped, or returns “No record found” if it finds no mapping for the key.

delete_val(key): Removes the mapping for the specific key, if the key is found mapped.


What makes a Hash Table different from a Hashmap?

Hash Table:

  •       They are synchronized and fast.
  •       Allow more than one null value
  •       They allow only one null key.

Hash Map:

  •       They are unsynchronized and slow.
  •       Null values or null keys are not allowed.


The search complexity of a hash map is O(1).


#Code for hash map implementation

>>class Node:
def __init__(self, key, value):
     self.key = key
     self.value = value
     self.next = None
>>class hashmap:
def __init__(self):
     self.store = [None for _ in range(n)]
def get(self, key):
     index = hash(key) & n-1                   
     if self.store[index] is None:
         return None
     p = self.store[index]
     while True:
         if p.key == key:
             return p.value
             if n.next:
                 p = p.next
                    return None
def put(self, key, value):
     nd = Node(key, value)
     index = hash(key) & n-1
     p = self.store[index]
     if p is None:
            self.store[index] = nd
         if p.key == key:
             p.value = value
             while p.next:
                 if p.key == key:
                        p.value = value
                        p = p.next
             p.next = nd
>>hm = hashmap()
>>hm.set("1", "red")
>>hm.set("2", "blue")
>>hm.set("3", "green")
>>hm.set("4", "yellow")
>>hm.set("5", "purple")




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